The present invention relates to a device for producing tooth impressions with a tray that can cover a plurality of adjacent tooth positions of a jaw, the contour of the tray roughly matching the contour of the jaw.
Such a device is described in DE 41 30 701 A1.
In practice no completely satisfactory tooth impressions are obtained with such a known device.
The present invention is therefore intended to provide an improved device for producing tooth impressions with a tray that can cover a plurality of adjacent tooth positions of a jaw, the contour of the tray roughly matching the contour of the jaw, so that extremely accurate impressions can be obtained.
This objective is achieved according to the invention by a device that has the following features: The free edges of the tray walls run so that they can form together with soft tissues of a patient""s mouth a sealing point, which tray is provided with at least one impression material connection element communicating with the interior of the tray, and with a source for liquid hardenable impression material that is connected to the impression material connection element, wherein the tray has at least one vacuum connection element communicating with the interior of the tray and that is connected to a reduced pressure source.
The following functions and advantages are achieved with a device according to the invention for producing tooth impressions:
The tray can be accurately positioned and firmly secured when used either on the upper jaw or on the lower jaw, and more specifically independently of mucous membrane activity or tongue movements. The tray does not need to be held by the dentist or by a dental assistant. Accordingly, not only are handling and manipulation substantially simplified, but the production of an impression is also less uncomfortable for the patient.
The tray is tightly sealed at the edge, so that no liquid impression material can escape from the tray and reach, for example, the throat.
On account of the fact that the impression space, which is bounded on the one hand by the tray and on the other hand by the patient""s teeth and the gums surrounding the teeth, is according to the invention subjected to a reduced (sub-atmospheric) pressure, the edges of the gums are retracted slightly from the neck of the teeth, so that the initially liquid impression material also forms a good impression of the region of the teeth lying adjacent to the edge of the gums.
The device according to the invention employs the closed impression space already referred to above. This space may, before being filled with an impression material or also in application situations not connected with making impressions, also be used for the selective application of therapeutic agents, especially in the form of liquids, aerosols or gases. Such agents may for example include haemostatics, wetting agents, astringents disinfectants, fluoride solutions, desensitizing substances, deodorants, flavouring agents, substances for periodontal treatment, substances for caries prophylaxis, substances preventing plaque formation, wetting agents such as sodium lauryl sulphate, anitadhesives in the form of liquid solutions or aerosols, for example Delmopinol or Triclosan solutions, agents for dealing with salivary gland secretions, or physical therapeutic agents such as water, warm air and the like.
The device according to the invention involves a directed flow of liquids, for example of the aforementioned therapeutic agents or of the impression compound, from the impression material connection element via a predetermined flow pathway to the vacuum connection element. These added liquids flush out any liquids such as saliva and blood that may be present on the aforedescribed flow pathway. In this way a complete filling of the impression space is ensured. The relative movement between the liquids and the longitudinal axes of the teeth takes place at an angle other than zero, preferably at an angle of 90xc2x0. In this way preferred flow directions can be established, from distal to mesial or vice versa, or from buccal to oral or vice versa. With the conventional impression techniques the tray filled with the impression material is mounted on the jaw in a direction perpendicular to the plane of the jaw, which means that the relative movement between the impression material and the teeth occurs parallel to the longitudinal axis of the teeth.
When using the device according to the invention the production of the tooth impression can also be combined with a therapeutic effect by for example adding a therapeutic agent to the impression material itself.
Also, various steps in the production of the impression can be combined, for example by adding, the wetting agent to the impression material itself instead of applying the wetting agent in a preparatory step to the surfaces of which an impression is to be made, or in the preparation of the material, thereby avoiding the need for this preparatory step.
The liquid hardenable impression materials that are used in the device according to the invention have a relatively high viscosity compared to water, typically that of the so-called xe2x80x9cthin-bodiedxe2x80x9d impression or correcting compounds that are used for intraoral impression work (in contrast to kneadable impression compounds). For this reason they arc added under a positive pressure to the impression material connection element, and the reduced pressure generated in the impression space is chosen so that, on the one hand, the desired good edge sealing of the tray and the desired good positioning of the tray is ensured, but on the other hand no haematomas are formed in the tissues cooperating with the edges of the tray and the patient is not subjected to severe discomfort or pain.
The applied reduced pressure and the feed pressure for the impression material as well as the filling amount per unit time and the viscosity of the impression compound are matched to one another. While the impression space is being filled the reduced pressure and the feed pressure are maintained substantially constant, so that the impression material fills the impression space at a uniform rate (and thus in particular without any interruption), the front of the impression material displacing forwardly any liquids (water, saliva, blood) present in the impression space. These liquids are then sucked out through the vacuum connection element. This continuous filling of the impression space ensures that no enclosed bubbles on xe2x80x9cshadowxe2x80x9d regions formed by teeth against the filling direction are obtained in the impression.
Alternatively, during the continuous filling of the impression space the reduced pressure may first of all be lowered and then raised somewhat towards the end of the filling procedure, the reduced pressure and/or the conveying pressure being controlled overall in such a way as to ensure a continuous flow of the impression material. Care is preferably taken to ensure that the impression material does not come to a stop within the tray.
The filling of the impression space under a vacuum, which in the device according to the invention preferably takes place perpendicularly to the longitudinal axis of the teeth, ensures in particular that full impressions can be made without any delay also of undercuts lying underneath the tooth equator and of gaps between the teeth. Also, impressions of the tooth surfaces are made in a largely pressure-free manner, thereby avoiding errors due to elastic reverse movement of the impression material or due to any eddy formations on sharp tooth edges, for example in the region of preparation edges.
Tooth impressions using the device according to the invention are produced with a high certainty of success, with savings in time, and in a way that is more pleasant for the patient. More precise tooth impressions are obtained than is the case with conventional techniques. This does not only mean that the impressions have smaller tolerances, but also that there is a better wetting of more surfaces, even of surfaces in difficultly accessible places.
As already mentioned above, in the use of the device according to the invention the movable marginal gingiva is retracted from the fixed adjacent tooth surfaces. In this way a good impression can be made directly of the region of the edge of the gum. This is particularly important when teeth are prepared for example to receive crowns. The preparation boundary frequently lies at the level of the edge of the gum (paramarginal) or even apically (in the direction of the root) of this region (subgingivally). For the purposes of complete coverage and for the necessary coverage of about 1 mm of the tooth root surface apically to the preparation boundary (essential for the correct contouring of the crown), when the device according to the invention is used the impression material is able to flow between the gum and tooth root surface.
This impression procedure is made possible by the previously described retraction of the edge of the gum under the acting vacuum, the already aforedescribed directed flow of the impression material also however being favourable since the liquid column (saliva or sulcus fluid) present in the gum sulcus or in gum pockets in the gap between the edge of the gum and tooth surface is displaced away from the impression material. Such a displacement does not occur with conventional impression techniques, since in these the teeth come into contact occlusally with the impression material, which means that the various sections of a gum edge of a tooth are coated more or less simultaneously with impression material. The liquid column lying between the edge of the gum and the tooth surface is thus enclosed, and since it cannot be compressed a corresponding bubble-like void is obtained in the finished impression, or the production or impressions of subgingivally lying tooth surfaces or prepared tooth surfaces is prevented.
It is understood that these tooth surfaces localised in the region of the marginal edge of the gum can, after drying in a current of air, also first of all be sprayed all over with a thin-bodied impression material before the tray according to the invention is inserted into the patient""s mouth. Following this first spraying the tray according to the invention is then mounted in position, a vacuum is applied, and the tray is filled with impression material. The impression material is chosen so that it is compatible with the initially applied thin-bodied impression material and combines with the latter during the course of the hardening. The impression material that was first of all sprayed on manually also serves at the same time as a space occupier that prevents refilling of deep pockets with liquids such as sulcus fluid or blood from the base of the pocket after it has previously been dried. In the aforedescribed procedure some of the material injected beforehand is displaced, while other parts mix thoroughly with the impression material introduced subsequently during the use of the tray according to the invention. Any bleeding that has occurred in the meantime is again displaced before the front of the impression material introduced into the tray and is sucked off at one of the vacuum connection elements. This procedure has proved effective for example in the case of patients with deep gum pockets and subgingival preparations.
It has proved particularly effective, before making the impression, to insert a retracting thread into the gum sulci preferably of the prepared or to be prepared teeth and to leave this in situ until after the impression has been made, whereby the production of impressions of paragingival or subgingival prepared teeth surfaces is furthermore simplified and made more precise using the method according to the invention.
Furthermore, the inflow of blood into the impression tray that is under a vacuum can be successfully avoided in this way, especially in the case of inflamed gingiva (gums), which have an increased tendency to bleed.
The retraction thread may be impregnated with therapeutically active substances, for example to stop bleeding.
In the case of teeth to be prepared having a preparation boundary to be paragingivally or subgingivally extended and exhibiting somewhat deeper gum pockets, it has proved particularly effective to insert one or more retraction threads above one another into the gum pockets before starting the preparatory work, in order thereby to prevent damage to the marginal gum edge by the preparation instruments, at least the most apical retraction thread remaining in situ until after the impression has been produced.
The reduced pressure source establishes a pressure drop in the range between 10 and 500 mbar, preferably between 10 and 200 mbar, and particularly preferably between 50 and 150 mbar. If the vacuum generated in the impression space is chosen according to this feature, then on the one hand this ensures a reliable positioning of the tray in the patient""s mouth, and on the other hand the forces exerted by the free edges of the tray on the soft tissue in the patient""s mouth are not so large as to cause the patient pain. The particularly preferred values for the reduced pressure produced in the impression space ensure that the gum edges are retracted slightly from the teeth, so that a good impression of the teeth in the gum region can be produced.
The reduced pressure source has a suction arrangement and a reduced pressure regulator connected in front of its suction opening. The development of the invention according to this feature permits the reduced pressure produced in the impression space to be adjusted in each case according to the circumstances of each patient. In particular the reduced pressure can be adjusted by visually monitoring the gum edge using an at least partially transparent tray, so that the gum edge retracts just a little.
The suction arrangement has a venturi nozzle whose feed inlet is connected to a compressed air line. The development of the invention according to this feature permits a reduced pressure of desired magnitude to be produced in a simple manner using compressed air that is of course available in a dentist""s surgery. The production, according to the venturi principle, of the reduced pressure required by the device according to the invention can also be employed in combination with an existing suction device in the surgery. Alternatively, the existing suction device in the surgery can also be used in conjunction with an additional reduced pressure regulator.
An impression material distributor tube extends in the longitudinal direction of a curved impression space predetermined by the tray, which tube has at least one opening, is preferably open at its ends, and preferably also has at least one outlet opening in the tube wall, open to the interior of the tray, an outlet opening pointing to the tooth position preferably additionally being provided for each tooth position. The development of the invention according to this feature enables a defined vacuum to be maintained in the impression space up to the end of the filling procedure.
The tray covers a whole tooth arch and has a symmetrical shape relative to a longitudinal centre plane, wherein the distributor is likewise symmetrical relative to the longitudinal centre plane of the tray and is extended by the two arms of the impression space having a U-shaped geometry in plain view. The development of the invention according to this feature is of advantage with regard to a rapid and uniform inflow of the impression material into the impression space.
The tray has a plurality of vacuum connection elements, which are preferably arranged symmetrically to its longitudinal centre plane. The same comments apply as regards the development of the invention according to this feature. By virtue of the fact that a plurality of vacuum connection elements (at least three) is arranged symmetrically relative to the centre plane, a complete filling of the impression space is ensured even in the case where the jaw relationships are asymmetric or where the patient has only a partial set of teeth. If towards the end of the filling procedure one or more of the vacuum connection elements is/are closed by impression material, then in addition a reduced pressure is produced and liquids displaced by the front of the impression material are suctioned off by the still free connection elements, so that the last phase too of the filling procedure takes place in a bubble-free manner.
At least some of the vacuum connection elements communicate with associated vacuum distributor lines, which extend over a plurality of teeth positions and have at least one suction opening, and preferably have a suction opening for each of the teeth positions. The development of the invention according to this feature is of advantage with regard to an even more uniform reduced pressure charging during the filling of the impression space and with regard to an even more uniform removal of liquids displaced in front of the impression material.
If a vacuum distributor line is used as proposed according to this invention, in conjunction with an impression material distributor line that is the subject matter of the invention, then flow directions of the impression material from buccal to oral or vice versa can be established, such flow patterns being able to be realised particularly effectively if aligned openings in the impression material distributor line and the vacuum distributor line are associated with each tooth position.
The vacuum connection elements are connected via a common reduced pressure line to the reduced pressure source. In a device according to this feature the various vacuum connection elements are likewise connected to a vacuum, which is also of advantage with regard to a rapid and uniform filling of the impression space. In practice the clear diameter of the vacuum connection elements is smaller than that of the common reduced pressure line. If impression material is drawn into a connection element because the tray is full at this point, only a part of this material is further aspirated, since on account of its high viscosity it can move only with difficulty in the narrow channel of the connection element. The corresponding vacuum connection clement is thus closed. The impression material cannot however flow into the common reduced pressure line, with the result that the other vacuum connection elements are in addition exposed to reduced pressure through this line. After closure of a vacuum connection element the flow pattern of the impression material is changed, more specifically by the fact that the impression material is added to the still unfilled sections of the impression space. The arrangement and number of the vacuum connection elements can be derived from a simplified model of the shape of the jaw, according to which the rows of side teeth up to the canine tooth are regarded as a straight line, and the front tooth region between the two canine teeth is regarded as a further straight line. The nodal points for the suction then lie in each case mesially with respect to the canine teeth between the canine tooth and the lateral incisor at the points of intersection of the straight lines, and in addition at least one nodal point is provided symmetrically between the two middle incisors.
The impression material connection elements and the vacuum connection elements are carried by a tray section formed as a disposable part, whereas the reusable remainder of the tray is formed as a sterilized part. The device according to this feature obviates the need for a costly cleaning of the connection elements. The reusable part of the tray may be manufactured from rigid or soft material. That part of the tray formed as a disposable part is preferably rigid and designed so that it is largely surrounded by the added impression material. This arrangement means that the tray assembled from the individual tray parts is overall stiff and torsionally rigid, while at the same time that part of the tray designed as a disposable part together with the hardened impression material forms a rigid part that can be sent to the dental laboratory, minus the reusable part of the tray. The use of a pliable reusable tray part is on the other hand advantageous having regard to a simple and inexpensive sealing between the tray parts. If desired, in addition only those sections of the tray segment designed as a disposable part, which lie adjacent to the gum, may be made of soft elastic material.
The impression material connection elements and the vacuum connection elements are carried by a central section of an external edge wall of the tray, the central section of the external edge wall, optionally in combination with the connection elements, preferably being formed as a handle. With a tray of the type disclosed in this feature, the various connection elements for impression material and the reduced pressure charging are arranged in a common front region of the tray, which simplifies the manufacture of the flow connections.
The impression material connection element is arranged in an apron of the external edge wall of the disposable tray part, which element engages in a complementary recess of the external edge wall of the reused tray part. According to this feature connection elements having a large flow cross-section may also be provided in a small front central region of the tray, these connection elements belonging to the part of the tray optionally designed as a disposable part.
The cooperating edges of the reused tray part and disposable tray part are sealed with respect to one another via a groove/tongue joint and/or a seal. According to this feature a good fluid seal is achieved between the reusable tray part and the disposable tray part. The impression space can therefore be subjected to a vacuum using a fairly weak suction arrangement. Alternatively or in addition, extra sealing compounds may also be provided at the points of contact between the tray segments, for example mouldable and/or hardening sealing compounds, for example silicone may be injected or plastic or plastically or elastically mouldable and hardening sealing compounds may be used, for example kneading compounds, silicones, waxes, plastics or the like. Furthermore, flexible tube-like sealing elements may be used at the points of contact between the tray parts.
The free edge of the tray carried an elastically flexible seal. The seal is carried by a bendable section of the disposable tray part. The seal is an expandable flexible hollow body that is connected to a compressed air source, or is an elastically deformable hollow body. The developments of the invention according to these features are advantageous having regard to an efficient, gentle sealing of the impression space involving the minimum of equipment.
The disposable tray part has at least one material longitudinal web running in the longitudinal direction of the impression space and a plurality of transverse webs running between the latter web and the external edge wall of the disposable tray part, the material longitudinal webs and the transverse webs being designed so that they permit a flow of the impression material in the longitudinal direction of the dental arch and/or a direction perpendicular thereto. If the disposable tray part is designed according to this feature then it can easily be handled as one unit, for example mounted on the reusable tray part, and moreover it still has a certain degree of flexibility in order that it can adapt to the shape of the reusable tray part so as to engage in a reliable frictional or snap-type manner with the latter. The weblike construction of the disposable tray part also saves material, which is particularly advantageous in the case of disposable tray parts.
The impression material distributor tube is connected to the tray edge part, and in particular is embedded wholly or partly therein. The development of the invention according to this feature ensures a precise positioning of the impression material distributor tube in the tray.
The tray is wholly or partly made of transparent material, in particular transparent plastics material, and in addition the vacuum connection elements are also preferably made of transparent material, in particular transparent plastics material. The development of the invention according to this feature enables on the one hand the correct mounting and positioning of the tray to be checked visually. Furthermore it can be checked visually whether the correct reduced pressure for the respective patient is set in the impression space (slight retraction of the gum edges). Finally, with a tray according to this feature the filling of the impression space with impression material can also be visually checked. The following features can furthermore be readily visually checked: the suction and removal of therapeutic agents or liquids such as blood or saliva from the impression space via the vacuum connection elements, as well as any blockage of the vacuum connection elements by aspirated impression material.
A section of the interior of the tray is separated by a sealing wall from the impression space, the free edge of the sealing wall being able to be placed tightly against the intraoral soft tissue, and that a separate suction line leads to the suction space bounded by the sealing wall, which suction line is connected to a separate vacuum connection piece that in turn is connected to a reduced pressure source, in particular to the reduced pressure source communicating with the impression space. The development of the invention according to this feature is advantageous having regard to a secure positioning of the tray in the patient""s mouth at all stages of the impression producing procedure.
The passage cross-section of the connection elements for the impression material corresponds to the area of a circle having a diameter of about 2 to 8 mm, preferably about 4 to 6 mm. If the diameter of the connection elements of the tray is chosen according to this feature, this ensures a good reduced pressure charging in the impression space as well as a good supply of impression material to the interior of the tray.
The impression material source provides the impression material under excess pressure, preferably an adjustable excess pressure. The development of the invention according to this feature ensures an even more rapid filling of the impression space combined with a high impression accuracy.
The impression material source provides an impression material containing a hardening catalyst, the catalyst being chosen and metered and the reduced pressure in the impression space and the discharge pressure of the impression material source being adjusted relative to one another so that the hardening of the impression material takes place only after the impression space has been completely filled. Also, the development of the invention according to this feature is advantageous having regard to a tooth impression that is uniformly accurate in all sections.
There is a rinse fluid source that can be connected to the impression material connection element. With a device according to this feature the tray can also be used in order to rinse the impression space with a rinse fluid or treatment fluid before filling the space with impression material or in treatment situations that do not involve the production of impressions. This rinsing, may be carried out with liquid media as well as gaseous media.
The rinse fluid source provides a fluid containing at least one active constituent, for example a liquid containing active constituents or an active constituent aerosol or a gas. According to this feature, in conjunction with this rinsing procedure active constituents may also be allowed to act on the tooth surfaces or tissues, for example cleansing agents, separating agents or haemostatic agents, as well as the other treatment agents specified hereinbefore.
An impression material locking element is arranged at or in the vacuum connection elements. The development of the invention according to this feature ensures in a particularly effective way that no impression material reaches the reduced pressure source.
The impression material locking element contains a filter element. A closure element for impression material, as is specified in this feature, can easily be realised as a disposable part using conventional components.
The impression material locking element contains additional hardener material and/or additional catalyst material. The development of the invention according to this feature ensures that any impression material in a somewhat liquid state that still reaches the closure element cannot be sucked into the reduced pressure source.
The impression material connection element has a closure means. With a device according to this feature the impression space can first of all be evacuated in order to position the tray, without already having to connect for this purpose the source of the liquid hardenable impression material. This facilitates the positioning of the tray.
The closure means is a valve or a sealing foil that is forcibly opened when the source for the liquid hardenable impression material is connected to the impression material connection element. According to this feature the closure for the impression material connection element is achieved at low cost, and a simpler opening of the impression material connection element is immediately automatically ensured on connecting the source for the liquid hardenable impression material.
The tube wall of the impression material distributor tube has a plurality of outlet openings spaced apart in the longitudinal direction, which differ at least in some cases in their diameter and/or their alignment. The tube walls of the vacuum distributor lines have a plurality of outlet openings spaced apart in the longitudinal direction, which differ at least in some cases in their diameter and/or their alignment. The developments of the invention according to these features are advantageous having regard to the creation of the flow pattern of the impression material in the impression space. Preferably this flow pattern is adjusted so that the front of the impression material moves towards a still uncovered vacuum connection element until the filling procedure is completed. This means that in the practically advantageous arrangement of the vacuum elements in the front region of the tray, the mould is filled from back to front.
The invention is intended for use in a dental laboratory. The good dimensional accuracy of impressions that are obtained with the device according to the invention can advantageously also be utilised in the dental laboratory when making copies of impressions or parts thereof, as is specified in this feature.
When using the impression tray in the dental laboratory or for making copies or for other purposes, if no saliva or blood has to be removed, and where perhaps there are no wet gum surfaces and well-defined material surfaces to be treated, then the use of active vacuum suction can also be omitted. The vacuum connection elements then serve to aerate the impression space. The filling of the impression space is accomplished by introducing impression material under positive pressure.
The same comments also apply if the tray and/or the impression producing system is used only to carry out treatment with therapeutic agents.
The invention has a tray base part and a distributor part mounted on its external wall, that the tray base part has in its external wall at least one impression material feed opening and/or at least one vacuum feed opening spaced therefrom, and that an impression material feed channel arrangement is provided in the distributor part, which arrangement connects the impression material connection element carried by the distributor part to the impression material feed openings, and/or a vacuum feed channel arrangement is provided, by means of which at least one vacuum connection element carried by the distributor part is connected to the vacuum feed openings. An impression tray according to this feature is particularly simple to manufacture since the tray base part has substantially the same design and construction as a conventional impression tray. The only difference is that some additional feed openings are provided in the external wall. The addition of impression material to the impression material feed openings and the vacuum charging of the vacuum feed openings is effected by means of a distributor part mounted on the tray base part, which distributor part may in practice be an injection moulding or casting and may be inexpensively provided with the necessary channels.
At least one vacuum feed opening is provided in the anterior end section of the tray base part. At least one impression material feed opening is arranged in a distal end section of the tray base part. The developments of the invention according to these features are advantageous having regard to a particularly good guidance of the impression material in a constant direction without inclusion of bubbles.
The sections of the channel arrangements of the distributor part adjacent to the feed openings are formed as open grooves up to the tray base part. If the various channel arrangements via which the vacuum and impression material are supplied to the main part of the tray are formed at least partially as open grooves, according to this feature, then the distributor part is particularly simple to manufacture. These grooves together with the external surface of the tray base part form closed channels. This design of the channel arrangement is also advantageous having regard to effective disinfection and sterilisation as well as ease of cleaning after use.
The tray base part and the distributor part have cooperating positioning means. The development of the invention according to this feature ensures a necessary correct arrangement and alignment of the feed openings and channel arrangements.
The positioning means have positioning grooves and positioning ribs, which extend in the vicinity of the edges of the external wall of the tray base part. If extended positioning means according to this feature are chosen, then these do not need to have very sharply defined projections and recesses, which would be disadvantageous as regards cleaning the tray base part and the distributor part. Nevertheless, a reliable alignment of the distributor part on the tray base part is ensured.
The distributor part is detachably connected by means of an catch connection to the tray base part. The development of the invention according to this feature enables the distributor part and the tray base part to be combined into a single manipulable unit, which facilitates insertion into the mouth. Moreover, this ensures that the distributor part and the tray base part can also easily be separated from one another, and in addition these parts may also be made of different materials and using simple moulds.
The boundary surface of the distributor part facing the tray base part has at least one suction pocket that is connected via a further channel arrangement of the distributor part to a separate vacuum connection element. The development of the invention according to this feature ensures an even more chargeable connection between the tray base part and the distributor part.
At least one section of the tray base part is made of transparent material. With an impression tray according to this feature the dentist can visually check the filling of the impression space with impression material.
The feed openings and the channel arrangements are symmetrical relative to a longitudinal centre plane of the impression tray. With an impression tray according to this feature the filling of the impression tray takes place symmetrically.
Two vacuum connection elements are provided in the anterior end section of the distributor part, which elements communicate via a section of the vacuum feed channel arrangement with a central vacuum feed opening and preferably with two lateral vacuum feed openings approximately at the height of the canine tooth position of the tray base part. The development of the invention according to this feature ensures that if there is an accidental unsymmetrical filling of the impression space (due for example to gaps between the teeth), then when the liquid impression material reaches one of the vacuum connection elements, liquids are suctioned off as before through the other one of the vacuum connection elements and the still unfilled section of the impression space is subjected to a reduced pressure. As a result, during the filling of the impression space there is always a controlled flow of the impression material directed to at least one active vacuum feed opening, the accurate flow direction being predetermined by the curvature of the jaw and the position of the tooth.
The external surface of the distributor part is spherical. The development of the invention according to this feature is advantageous having regard to an overall sealing of the impression space area. The impression space is thus sealed not by the edges of the impression tray, but by soft tissue lying flat against the outside of the distributor part.
The tray base part and/or the distributor part is a plastics moulding. The development of the invention according to this feature is advantageous having regard to an inexpensive manufacture of the tray base part and the distributor part. These parts may be made as disposable parts if so desired.
The tray base part and/or the distributor part is a metal moulding. If the parts of the impression tray are made according to this feature of metal, then these parts can be sterilised and reused.
The various connection elements are arranged closely adjacent in the anterior end section of the distributor part. The development of the invention according to this feature enables all connection joints between the impression tray and vacuum source and/or impression material source to be effected by a single multiple connector. This simplifies the use of the impression tray.
The vacuum feed channel arrangement has, looking in the flow direction, at least one impression material lock in front of at least one vacuum feed opening. With the development of the invention according to this feature, at least one of the vacuum feed openings is in communication with a vacuum connection piece up to the completion of the filling of the impression space. This development also prevents closed channels of the distributor part being filled with impression material, which could be removed only with great difficulty.
The impression material locks are in each case formed by a raised section of the floor of a distributor groove, which is part of the vacuum feed channel arrangement. According to this feature an impression material lock can be produced in a particularly simple manner during the injection moulding, casting or machining of the distributor part.
The tray has a feed opening communicating with a first end of the impression space and a second feed opening communicating with a second end of the impression space. With the development of the invention according to this feature the impression material successively fills, starting from one end and going to the other end, the mould space bounded by the tray and soft tissues. The addition of impression material can then be stopped once a particular part of the dentition in question is surrounded by impression material, by visually checking the movement of the front of the impression material. The rest of the impression space remains unfilled. A significant saving in impression material is achieved in this way.
In the dental laboratory it is sometimes necessary to produce a negative mould from a tooth model that was made starting from a tooth impression or from models with intermediate stages mounted thereon in the production of replacement teeth or in teeth restoration work, prostheses, implants, explants, etc. This work is termed copying or replication.
In the present description the term copying should generally be understood to mean making copies of arbitrary surface sections of dental, dental-medical or medical objects, in particular moulded bodies, outside the mouth, for example of sections of model surfaces or replacement tooth surfaces or prosthesis surfaces, implant surfaces, explant surfaces, etc. If very accurate model impressions obtained by copying are required, similar problems to those that arise in making impressions of teeth are encountered. The device according to the invention for producing tooth impressions can therefore also be used to produce model impressions, and accordingly in copying. Of course, in addition to the tray a cavity or lower mould is also required that is comparable as regards its mechanical properties to the soft tissues in a patient""s mouth, and can therefore define in particular together with the tray a flow medium-tight impression space. A device with such a cavity mould constitutes the subject matter of the following feature: there is a cavity mould on which an object of which an impression is to be made can be secured, and which has a preferably deformable sealing wall surrounding the object of which an impression is to be made, which together with the tray defines a sealed impression space.
The sealing wall has a sealing membrane secured on a housing of the cavity mould. This feature discloses a particularly simple way and means of preparing a sealing wall that accurately matches the edge contour of the tray.
The sealing membrane together with the housing defines a membrane rear space that is filled with a fluid. The development of the invention according to this feature enables the deformability of the sealing wall to be modified in a simple way, by altering the nature or the pressure of the fluid lying behind the sealing membrane.
The corresponding variants are disclosed in the following features: the fluid is a gas under reduced pressure, whereby the sealing membrane is prestressed into a concave shape; the fluid is a liquid or a gel; and there is a pressure regulator communicating with the membrane rear space.
The sealing wall comprises elastically deformable material. According to this feature a sealing wall is also obtained that can accurately match the edge contour of the tray, this sealing wall requiring no separate clamping arrangement or indeed any connection to a vacuum or pressure source.
The free front surface of the foam material has a tight surface skin or carries a film impermeable to flow media. The development of the invention according to this feature is advantageous having regard to a particularly simple construction and fluid-tightness of the sealing wall.
The tray has an external circumferential wall that is adjustable as regards height. The development of the invention according to this feature enables impressions to be made from models of different heights, with a saving in the use of impression material.
The circumferential wall has a stationary wall part and a vertically movable wall part in a groove of the latter, as well as means for predetermining the spacing between the movable wall part and stationary wall part. The development of the invention according to this feature enables the height of the tray to be continuously adjusted.
The movable wall part is pretensioned in an extended position by means of a spring arrangement. If the tray is designed according to this feature, it always adopts the same position in the state in which it is not yet mounted on the mould lower part. This facilitates a precise positioning and furthermore protects the sealing wall of the mould lower part when the tray is mounted.
The movable wall part is sealed by a sealing arrangement against the groove of the stationary wall part. The development of the invention according to this feature ensures that no impression material reaches the guide for the movable wall part.
The tray is a one-pieced disposable part made of plastics material, in particular a deep-drawn part. The development of the invention according to this feature is advantageous having, regard to ensuring hygienic conditions without the use of sterilisation processes.
At least one feed opening of the tray that can be connected to a vacuum source is arranged in an, under operating conditions, upper wall section of the tray. The development of the invention according to this feature serves for a bubble-free complete filling of the impression space.
At least one of the feed openings is provided in an, under operating conditions, rear wall of the tray. The development of the invention according to this feature enables the impression material, in the production of model impressions, to flow in from the rear end of the model without having to provide the tray with a system of channels.
If the tray used for making the impressions is rigid, then a strictly predetermined amount of impression material is required to produce an impression. The tray has a bowl-shaped rigid tray housing and an elastically deformable impression space membrane secured to the latter. When using a tray according to this feature the impression space membrane partially defining the impression space can be matched as regards its geometry to the space occupied by the model, so that the impression includes only the space regions of interest that are immediately adjacent to the model.
There are means for contouring the impression space membrane. With the development of the invention according to this feature a pre-contouring is imparted to the impression space membrane.
The contouring means have a contoured supporting element and means for pretensioning the impression space membrane against the supporting element. With the development of the device according to this feature the pre-contouring of the impression space membrane can be reproduced very accurately.
The supporting element is lattice-like or open-pore and the pretensioning means have a reduced pressure source that can be connected to the working space bounded by the impression space membrane and the tray housing. According to this feature the impression space membrane is urged flat against the contoured supporting element by applying a reduced pressure.
The pretensioning means have a pressure source that can be connected to the impression space in front of the impression space membrane. According to this feature the same advantage is obtained using an excess pressure source, in which connection the latter may for example be an impression material source that delivers the impression material under excess pressure.
The tray has an impression space membrane running over the model and means are provided for subjecting different regions of the impression space membrane to different loads, the impression space membrane preferably being secured to a lower section of a housing of the cavity mould. Also, the development of the invention according to this feature permits a simple matching of the geometry of the impression space to the size of a model of which an impression is to be produced.
The loading means have weights adapted to different regions of the model. According to this feature the force that the membrane exerts against the added impression material can be predetermined in a simple way, and the wall thickness of the impression can be varied by selecting different weights.
The loading means have at least one position indicator cooperating with one of the weights. According to this feature the manner in which the impression material increasingly flows round the model can be measured, and after the material has reached a predetermined height above the tip of the model the addition of further impression material can be stopped.
There is at least one dead space element inserted in the tray, which is chosen from a plurality of standard dead space elements or is plastically deformable. Also, the development of the invention according to this feature is advantageous having regard to savings in the use of impression material, particularly when producing partial impressions that extend over only a part of a jaw.